Nutrient requirements of the lactating sow

The allowances given in the tables of Appendix 2 do not include a safety margin. 

Ewes that have been severely undernourished in pregnancy show a more rapid decline in milk production during the subsequent lactation than adequately nourished animals. This accords with independent observations of reduced metabolic capacity in ewes severely undernourished during pregnancy. Where restriction is less severe and ewes come to parturition in lean condition, they have been shown to milk as well when adequately nourished as do ewes with better condition scores at lambing. Ewes will not maintain high milk production at the expense of body reserves, and even relatively small restrictions of intake depress milk production. Severe restriction of nutrient intake (to provide maintenance only) may reduce milk production by as much as 50 per cent in 2-3 days. If restriction is continued beyond the time when peak yield is normally achieved, then recovery of yield may not be accomplished even if subsequent intake is raised. 

In most breeding units, lactation lasts for 3 weeks and many litters are weaned at 3-4 weeks of age. Maximum yield of milk occurs at about 4 weeks and production falls gradually thereafter, as shown in Table 16.17. 

Fat content rises to the third week and then falls to the end of lactation. Solids-not-fat content is at a minimum at the third week and then rises to the end of lactation owing mainly to a rise in protein content. 

Milk yield also varies with breed, age and litter size. It increases with the number of piglets suckled, although yield per piglet decreases as shown in Table 16.18. 

---